Abstract: This study aimed to investigate the effects of colloidal silica nanoparticles Aerosil 200 (A200) on intestinal barrier and mucosal immunity in childhood mice. Three-week-old BALB/c mice were administered A200 (20, 50, 200 mg·kg^-1) via gavage for 7 days. Intestinal morphology, barrier function, immune cell phenotypes, and oral tolerance were systematically evaluated. Histopathological analysis of intestinal morphology revealed that no obvious pathological damage in the intestine. However, 200 mg·kg^-1 A200 increased ileal villus length, reduced crypt depth. Functional assessments of the intestinal barrier demonstrated that 200 mg·kg^-1 A200 upregulated ZO-1 in the ileum but downregulated it in the colon; The intestinal stem cell marker Lgr5 remained unchanged, while Mucin-2 increased and lysozyme decreased in the ileum. Analysis of immune cell phenotypes revealed that the 200 mg·kg^-1 group exhibited elevated proportions of Treg and Th2 cells in the mesenteric lymph nodes, while serum and intestinal levels of TNF-α and IL-6 remained unaffected. Oral tolerance assays revealed no alteration in OVA-specific IgG, IgG1, or IgG2a antibody levels. Animal welfare and the animal experimental protocols were strictly consistent with related ethics regulations of Peking University Health Science Center (Approval No.: BCJB0076). In conclusion, A200 is generally safe for childhood mice but may modulate epithelial barrier proteins and immune cell phenotypes at high doses, which may provide insights into its pediatric application.